As shown in FIG. 4, a stator of a rotating electric machine (in particular, a high-voltage rotating electric machine) includes a stator coil 11 housed in a plurality of slots 16 formed on an inner peripheral side of a stator core 10. The stator coil 11 is constituted by a coil conductor 12 and an insulating coating 13. The stator coil 11 is manufactured by wrapping an insulating tape, which is formed by gluing a fibrous reinforcing material such as glass cloth to a mica sheet, several times around the coil conductor 12, impregnating the resulting component with a resin composition under reduced pressure, and then applying hot-pressing to the resulting component while molding the component into a predetermined sectional shape. Two stator coils 11 are incorporated into upper and lower portions of the slot 16. A spacer 15 is provided between the stator coils 11, and a wedge 14 is provided in an open end portion of the slot 16. As a result, electromagnetic vibration generated from the stator coils 11 during operation of the rotating electric machine is suppressed.
In a stator of a rotating electric machine having this type of structure, the conductor coil 12 generates heat in response to a load current generated during operation of the rotating electric machine. In an indirect hydrogen-cooled rotating electric machine in particular, a majority of the heat generated from the conductor coil 12 is transmitted to a cooling gas via the stator core 10. Hence, to achieve an improvement in efficiency and reductions in size and cost in the rotating electric machine, the thermal conductivity of the insulating coating 13 of the stator coil 11 must be increased.
To increase the thermal conductivity of the insulating coating 13 of the stator coil 11, use of an insulating tape that includes a filler exhibiting high thermal conductivity has been proposed (see Patent Document 1, for example).